1. Field of the Invention
The present invention generally relates to a fuel evaporative emission control system for preventing or suppressing evaporative emission of a fuel gas which is generated or produced within a fuel tank of an internal combustion engine for a motor vehicle or the like. More particularly, the present invention is concerned with an abnormality detecting apparatus for detecting occurrence of abnormality such as leakage or leak of the fuel gas in the fuel evaporative emission control system.
2. Description of Related Art
In general, in the internal combustion engine for motor vehicles or the like, it is statutorily imposed to equip the engine with a fuel evaporative emission control system with the aim of suppressing or preventing evaporative emission of the fuel gas produced within a fuel tank to the atmosphere. Incidentally, this system is also known as the fuel evaporative emission suppressing (or preventing) system.
The fuel evaporative emission control system of the type known heretofore is composed of a sensor means for detecting operation states of the internal combustion engine such as rotation speed, load state and others of the engine, a purge passage for communicating the fuel tank provided for supplying the fuel to the engine and an intake pipe thereof with each other and a canister disposed in the purge passage at an intermediate location thereof.
The canister adopted for adsorbing the fuel gas produced within the fuel tank has an atmospheric air port which can be opened to the atmosphere, wherein a purge control valve is disposed at an intermediate location between the canister and the intake pipe of the engine. An adsorbent disposed within the canister adsorbs the fuel gas on the way of flowing through the purge passage through which the fuel tank and the intake pipe are placed in communication.
Further, the fuel evaporative emission control system includes a fuel evaporative emission control means (usually constituted by a microcomputer or microprocessor) for controlling opening/closing operation of the purge control valve in dependence on the operation states of the internal combustion engine in order to sustain the fuel gas adsorbing function of the canister by preventing the adsorbent from becoming saturated.
The fuel evaporative emission control means is so designed or programmed as to control opening/closing of the purge control valve in dependence on the operation states of the internal combustion engine for causing the fuel gas adsorbed by the canister to be discharged into the intake pipe so that the fuel gas is mixed with the mixture of air and fuel to be subsequently fed to the engine. In this manner, the evaporative emission of the fuel can be avoided.
Ordinarily, in the fuel evaporative emission control system such as described above, the purge passage is constituted by a rubber hose which fluidally interconnects the canister and the intake pipe. Accordingly, if the rubber hose should be bent or collapsed, there will arise such unwanted situation that the fuel gas can not satisfactorily be introduced into the intake pipe and hence the amount of the fuel gas retained within the canister will exceed the fuel gas adsorbing capability of the adsorbent accommodated within the canister, which will naturally result in discharging of the fuel gas to the atmosphere through the atmospheric air port of the canister without the fuel gas being recirculated to the intake pipe, giving rise to a problem.
Furthermore, since the rubber hose is placed in contact with alcohol component of the fuel, there undesirably exists the possibility of the rubber hose being damaged due to corrosion. Besides, in the case where the atmospheric air port of the canister should get clogged with dusts, the rubber hose will be detached under the effect of increasing of pressure. In either case, the fuel gas will unwontedly be discharged to the atmosphere, giving rise to a problem.
For coping with the above-mentioned problems by detecting the abnormal situation such as described above, there has already been proposed an abnormality detecting apparatus which is so arranged as to detect or determine occurrence of abnormality in the fuel evaporative emission control system when the pressure prevailing within the fuel tank as detected by an associated pressure sensor exceeds a permissible maximum pressure level and/or when a predetermined pressure difference is not detected before and after changeover of the purge control valve between the opened state and the closed state. For more particulars, reference should be made to, for example, Japanese Patent Application Laid-Open Publication No. 125997/1993 (JP-A-5-125997).
With the conventional abnormality detecting apparatus disclosed in the publication cited above, it is certainly possible to detect positively and accurately the blockage of the atmospheric air port of the canister, impossibility of opening the purge control valve, damage and/or fall-off of the hose serving as the purge passage on the side of the intake pipe. It is however noted that in the abnormality detecting apparatus mentioned above, the purge rate is determined without taking into consideration the intake pressure (i.e., pressure prevailing within the intake pipe) and the remaining fuel quantity at the time point when abnormality decision enabling conditions are validated (i.e., when the conditions for enabling or allowing the decision as to occurrence of abnormality are satisfied, to say in another way). Consequently, a lot of time will be taken for determining the abnormality, being accompanied with the possibility of erroneous detection of abnormality, for the reason that smooth and speedy lowering of the fuel tank pressure upon abnormality detection is hindered by flow resistance encountered within the purge passage and a variable void volume of the fuel tank.
On the other hand, there may also arise such situation that the fuel tank pressure lowers excessively although it depends on the flow resistance within the purge passage and the void volume of the fuel tank, which may result in that the fuel tank is deformed or collapsed under the effect of excessively high negative pressure.
Additionally, it is noted that in the above-mentioned abnormality detecting apparatus for the fuel evaporative emission control system, concentration of the fuel gas which flows into the intake pipe from the canister is not taken into account in establishing the abnormality decision enabling conditions. Consequently, when the concentration of the fuel gas flowing into the intake pipe of the engine is high, there arises the possibility that the engine operation becomes out of order.
Under the circumstances, there has been proposed an abnormality detecting apparatus which includes an abnormality detecting means for detecting abnormality of the fuel evaporative emission control system on the basis of the pressure within the fuel tank (hereinafter also referred to as the fuel tank pressure) and a purge rate regulating means for adjusting or regulating the purge rate in dependence on the pressure prevailing within the intake pipe (hereinafter also referred to as the intake pressure) at the time when the abnormality decision enabling conditions are validated, as is disclosed in, for example, Japanese Patent Application Laid-Open Publication No. 296753/1997 (JP-A-9-296753).
For having better understanding of the concept of the present invention, description will be made in some detail of the abnormality detecting operation carried out by the abnormality detecting apparatus disclosed in the publication cited just above. FIG. 22 of the accompanying drawings shows a flow chart for illustrating the abnormality detecting operation of the abnormality detecting apparatus now concerned.
Referring to FIG. 22, decision is first made in a step S101A as to whether the concentration of the fuel gas (hereinafter also referred to as the fuel gas concentration) as detected by resorting to an appropriate method (see JP-A-9-296753 for more particulars) is higher or lower than a predetermined concentration. When it is decided that the fuel gas concentration is higher than the predetermined concentration, it is then determined in a step S101D that the abnormality decision enabling conditions are to be invalidated (i.e., unsatisfied), whereon the processing routine shown in FIG. 22 is terminated.
By contrast, when the decision in the step S101A results in that the fuel gas concentration is lower than the predetermined concentration, other conditions are checked in a step S101B. If the other conditions are valid, then it is determined in a step S101C that the abnormality decision enabling conditions are to be validated, whereon the processing routine shown in FIG. 22 is terminated.
As is apparent from the above, the concentration of the fuel gas introduced into the intake pipe from the canister is detected. Unless the fuel gas concentration is lower than the comparison reference value, it is determined that the abnormality detection enabling conditions for the fuel evaporative emission control system is invalid, i.e., not satisfied. Only when the abnormality detection enabling conditions are valid, the fuel tank pressure can be lowered to a desired or target pressure level with high accuracy, whereby the abnormality decision for the fuel evaporative emission control system can be performed speedily and accurately.
However, because the abnormality detection enabling conditions are determined to be invalidated on the basis of only the result of comparison between the fuel gas concentration and the reference value therefor, there may arise a problem that the validity of the abnormality detection enabling conditions can not always be determined with high reliability.
By way of example, the evaporative emission of the fuel within the fuel tank is easy to take place when the engine is operated in a highland region (where the atmospheric pressure is low) while it is difficult to occur in a lowland region (where the atmospheric pressure is high) even for a same fuel gas concentration level. However, since such influence of the atmospheric pressure is not taken into consideration, the abnormality detection performance in the highland region (where the atmospheric pressure is low) tends to degrade.
By contrast, in the lowland region (where the atmospheric pressure is high), the abnormal state may erroneously be detected.
Similarly, the evaporative emission of the fuel from the fuel tank will vary under the influence of the fuel temperature, the outside air temperature, the intake air temperature and the like even for a same fuel gas concentration level. However, such influence of the temperatures is not considered either, which will incur degradation of the abnormality detection performance as well as erroneous abnormality detection.
Additionally, it is noted that susceptibility of the fuel to the evaporative emission from the fuel tank varies in dependence on the degree of leak abnormality of the fuel evaporative emission control system such as fall-off of a cap of the fuel tank, detachment of the pipe serving as the purge passage or the like. However, variation of the fuel gas concentration in dependence on the degree of leak abnormality is not taken into account in the case of the abnormality detecting apparatus disclosed in the second mentioned publication. Consequently, when remarkable leak abnormality takes place due to fall-off of the cap of the fuel tank, the fuel evaporative emission becomes easier to take place, increasing the fuel gas concentration, which makes it difficult to inhibit or disable the abnormality detection (invalidate the abnormality detection enabling conditions) on the basis of the fuel gas concentration.
Moreover, since the susceptibility of fuel to the evaporative emission from the fuel tank changes in dependence on the atmospheric pressure, the outside air temperature and the like factors, the fuel tank pressure increases only slowly in the low temperature state while increasing rapidly in the high temperature state even for a same leak abnormality during a hermetical closure time period set for the purpose of detection of occurrence of abnormality in the fuel evaporative emission control system. However, in the abnormality detecting apparatus disclosed in the second mentioned publication, the rate of change of the fuel tank pressure is not considered either, and the hermetical closure time period is set to be constant, which may unwantedly lead to degradation of the abnormality detection performance.
As can now be appreciated from the foregoing, in the conventional abnormality detecting apparatuses for the fuel evaporative emission control system known heretofore such as the one disclosed in, for example, Japanese Patent Application Laid-Open Publication No. 296753/1997 (JP-A-9296753) which is considered as one of the most improved apparatus, the comparison reference value for determining the validity of the abnormality detection enabling conditions is set to be constant. As a consequence, the abnormality detection performance undergoes degradation under the influence of variation of the various environmental conditions, which may ultimately lead to impossibility of detecting the abnormality with high accuracy and reliability, thus giving rise to a problem.
Besides, since the hermetical closure time period for the abnormality detection is set constant, there may arise the problem that degradation of the abnormality detection performance is incurred.
In the light of the state of the art described above, it is an object of the present invention to provide an abnormality detecting apparatus for a fuel evaporative emission control system which can enjoy enhanced reliability by virtue of such arrangement that the comparison reference value for determining validity of the abnormality detection enabling conditions is set variable in dependence on various environmental conditions and the like.
Another object of the present invention is to provide an abnormality detecting apparatus for a fuel evaporative emission control system which can enjoy high reliability owing to such arrangement that the hermetical closure time period for the abnormality detection is set variable in dependence on the various environment conditions and the like.
In view of the above and other objects which will become apparent as the description proceeds, there is provided according to a general aspect of the present invention an abnormality detecting apparatus for detecting occurrence of abnormality in a fuel evaporative emission control system for an internal combustion engine, which apparatus includes sensor means for detecting engine operation states including rotation speed and load state of the internal combustion engine, a purge passage for communicating a fuel tank supplying a fuel to the internal combustion engine and an intake pipe thereof with each other, a canister disposed at an intermediate location of the purge passage for adsorbing a fuel gas generated within the fuel tank, an atmospheric air port provided for the canister and opened to the atmosphere, a purge control valve disposed intermediately between the canister and the intake pipe, and a fuel evaporative emission control means for suppressing evaporative emission of the fuel by controlling opening/closing of the purge control valve in dependence on operation states of the internal combustion engine and introducing the fuel gas adsorbed by the canister into the intake pipe as occasion requires.
The sensor means includes an intake pressure detecting means for detecting an intake pressure information representing a load state of the internal combustion engine, at least one of an atmospheric pressure detecting means for detecting an atmospheric pressure, an outside air temperature detecting means for detecting an outside air temperature, an intake-air temperature detecting means for detecting an intake air temperature of the internal combustion engine, and a fuel temperature detecting means for detecting a fuel temperature within the fuel tank, a fuel tank pressure detecting means for detecting a pressure within the fuel tank as a fuel tank pressure, a fuel-gas concentration detecting means for detecting concentration of the fuel gas introduced into the intake pipe from the canister, an air port blocking means for closing the atmospheric air port, a hermetically closing means for closing both the purge control valve and the atmospheric air port to thereby place the fuel evaporative emission control system as a whole in a hermetically closed state, an abnormality decision enabling condition detecting means for determining validity of abnormality decision enabling conditions for allowing decision to be made as to occurrence of abnormality in the fuel evaporative emission control system on the basis of the operation state of the internal combustion engine in the case where the fuel gas concentration is lower than a reference value for comparison, a purge rate regulating means for regulating a purge rate by controlling an opening degree of the purge control valve in dependence on the intake pressure when the abnormality decision enabling conditions are valid, and an abnormality detecting means for detecting abnormality of the fuel evaporative emission control system on the basis of the fuel tank pressure which has dependency on the purge rate when the abnormality decision enabling conditions are valid.
The abnormality decision enabling condition detecting means includes a condition validation limiting means for limiting validation of the abnormality detection enabling conditions by correcting the reference value for comparison in dependence on at least one of the atmospheric pressure, the fuel temperature, the outside air temperature and the intake air temperature.
In a mode for carrying out the invention, the condition validation limiting means may preferably be so designed as to correct the comparison reference value such that the comparison reference value is decreased when at least one of the atmospheric pressure, the fuel temperature, the outside air temperature and the intake air temperature changes such that the evaporative emission of the fuel is promoted.
In another mode for carrying out the invention, the abnormality decision enabling condition detecting means may preferably be so designed as to set distinctively a first comparison reference value and a second comparison reference value, respectively, for a first abnormal state and a second abnormal state which can be presumed on the basis of the fuel tank pressure and change over the first comparison reference value and the second comparison reference value in dependence on the first abnormal state and the second abnormal state, respectively.
In yet another preferred mode for carrying out the invention, the first abnormal state corresponds to a large-hole-leak abnormality while the second abnormal state corresponds to a small-hole-leak abnormality, wherein the abnormality decision enabling condition detecting means may be so designed as to set the second comparison reference value employed for detecting the second abnormal state to be smaller than the first comparison reference value employed for detecting the first abnormal state.
In still another mode for carrying out the invention, the hermetically closing means may preferably be so designed as to set changeably a hermetical closure time period during which the fuel evaporative emission control system as a whole is placed in a hermetically closed state in dependence on at least one of the atmospheric pressure, the fuel temperature, the outside air temperature and the intake air temperature.
In a further mode for carrying out the invention, the hermetically closing means may preferably be so designed as to set distinctively a first hermetical closure time period and a second hermetical closure time period, respectively, for a first abnormal state and a second abnormal state which can be presumed on the basis of the fuel tank pressure and change over the first hermetical closure time period and the second hermetical closure time period in dependence on the first abnormal state and the second abnormal state, respectively.
In a yet further preferred mode for carrying out the invention, the first abnormal state corresponds to a large-hole-leak abnormality while the second abnormal state corresponds to a small-hole-leak abnormality, wherein the hermetically closing means may be so designed as to set the second hermetical closure time period employed for detecting the second abnormal state to be shorter than the first hermetical closure time period employed for detecting the first abnormal state.
By virtue of the arrangements described above, there can be realized the abnormality detecting apparatus for the fuel evaporative emission control system which can ensure enhanced reliability and accuracy for the decision of occurrence of abnormality event in the system.
The above and other objects, features and attendant advantages of the present invention will more easily be understood by reading the following description of the preferred embodiments thereof taken, only by way of example, in conjunction with the accompanying drawings.